The present invention relates to a flame-retardant polycarbonate resin composition. Precisely, the invention relates to a flame-retardant polycarbonate resin composition and its moldings, which do not contain halogen but contain minor additives to exhibit good flame retardancy, and which have good impact resistance, good stability to molding heat, good wet heat resistance and good recyclability, and are resistant to static electrification.
As having the advantages of impact resistance, heat resistance, good electric properties and dimensional stability, polycarbonate resins have many applications in various fields of, for example, OA (office automation) appliances, information and communication appliances, other electric and electronic appliances for industrial use and household use, automobile parts and building materials. As a rule, polycarbonate resins are self-extinguishable. However, in some fields of typically OA appliances, information and communication appliances, and other electric and electronic appliances, it is desirable that the level of the flame retardancy of the products is increased for ensuring further safety of the products.
For improving the flame retardancy of polycarbonate resins, halogen-containing flame retardants such as bisphenol A halides and halogenated polycarbonate oligomers have been used along with a flame retardation promoter such as antimony oxide, as their flame-retarding ability is good. However, with the recent tendency toward safety living and environmental protection from discarded and incinerated wastes, the market requires flame retardation with non-halogen flame retardants. Polycarbonate resin composition containing, as a non-halogen flame retardant, any of phosphorus-containing organic flame retardants, especially organic phosphate compounds have good flame retardancy. In addition, organic phosphate compounds serve as a plasticizer, and various types of compositions containing them have been proposed.
In order to make polycarbonate resins have good flame retardancy by adding thereto a phosphate compound, a relatively large amount of the compound must be added to the resins. In general, polycarbonate resins require relatively high molding temperatures, and their melt viscosity is high. Therefore, for molding them into thin-walled and large-sized moldings, the molding temperature will have to be further higher. For these reasons, phosphate compounds often cause some problems when added to such polycarbonate resins, though their flame-retarding ability is good. For example, phosphate compounds often adhere to molds used for molding resins containing them, and generate gas to have some unfavorable influences on the working environments and even on the appearance of the moldings. Another problem with phosphate compounds is that, when the moldings containing them are left under heat or in high-temperature and high-humidity conditions, the compounds lower the impact strength of the moldings and yellow the moldings. On the other hand, the recent tendency in the art is toward recycling resin products for saving natural resources. However, as not stable under heat, phosphate compounds are against the requirement for recycling resin products containing them. This is still another problem with phosphate compounds.
Apart from the above, known is another technique of adding silicone compounds to polycarbonate resins to make the resins have flame retardancy. In this, silicone compounds do not give toxic gas when fired. For example, (1) Japanese Patent Laid-Open No. 139964/1998 discloses a flame retardant that comprises a silicone resin having a specific structure and a specific molecular weight.
(2) Japanese Patent Laid-Open Nos. 45160/1976, 318069/1989, 306265/1994, 12868/1996, 295796/1996, and Japanese Patent Publication No. 48947/1991 disclose silicone-containing flame-retardant polycarbonate resins. The level of the flame retardant disclosed in (1) is high in some degree. The technology of (2) differs from that of (1) in that the silicones used in (2) do not act as a flame retardant by themselves, but are for improving the drip resistance of resins, and some examples of silicones for that purpose are mentioned. Anyhow, in (2), the resins indispensably require an additional flame retardant of, for example, phosphate compounds or salts of Group 2 metals.
Japanese Patent Laid-Open No. 176425/1996 discloses a method of using an organic alkali metal or alkaline earth metal salt and a polyorganosiloxane for improving the flame retardancy of polycarbonate resins without detracting from the transparency thereof. In this, however, the flame retardancy of the resin compositions could be improved, but the impact resistance thereof is often lowered.
Japanese Patent Laid-Open No. 172063/1999 discloses a flame-retardant thermoplastic resin material for molding, which comprises (A) from 1 to 99 parts by weight of an aromatic vinyl resin having an acidbase such as an alkali metal sulfonate, and (B) from 1 to 99 parts by weight of a thermoplastic resin except (A); and a flame-retardant thermoplastic resin material for molding, which comprises 100 parts by weight of the resin mixture of (A) and (B), and from 0.1 to 100 parts by weight of a flame retardant (C) added thereto. Concretely, it discloses  less than 1 greater than  a molding material comprising 90 parts by weight of (A) and 10 parts by weight of (B) GPSS [polystyrene]; and  less than 2 greater than  a molding material comprising 10 parts by weight of (A), 80parts by weight of (B) PPE [polyphenylene ether] and 10 parts by weight of (C) TPP [triphenyl phosphate].
The laid-open patent publication shows the case  less than 1 greater than  in which the content of the aromatic vinyl resin having an acid base such as an alkali metal sulfonate is 90% by weight and is extremely large, and the case  less than 2 greater than  in which the content of the resin is 10% by weight and is small and the resin is combined with the additional flame retardant. In other words, when the content of the component (A) is small therein, the molding material is not resistant to flames. Accordingly, as is obvious from Comparative Example 1 therein, the component (A) alone cannot be molded into shaped articles. The serious problem with the technique disclosed is that a large amount of an aromatic vinyl resin having an acid base such as an alkal metal sulfonate must be used therein. Accordingly, the moldings obtained therein could be self-extinguishable and resistant to flames, but their physical properties intrinsic to thermoplastic resin would be significantly worsened.
In the current situation as above, the object of the present invention is to provide a flame-retardant polycarbonate resin composition containing a non-halogen flame retardant enough to ensure good flame retardancy and capable of being formed into good moldings which have good impact resistance, good thermal stability and good wet heat resistance intrinsic to polycarbonate resin, and which are recyclable and are resistant to static electrification; and to provide such moldings of the composition.
To attain the object of the invention, we, the present inventors have assiduously studied to find out additives that may serve as a flame retardant for polycarbonate resins, not detracting from the impact resistance, the heat resistance and the recyclability of the resin moldings containing them. As a result, we have found that, when a small amount of an acid base-containing aromatic vinyl resin is combined with a drip inhibitor and when the resulting combination is added to polycarbonate resin, then the resulting polycarbonate resin composition has good flame retardancy and its moldings have good impact resistance, good heat resistance and good wet heat resistance and are resistant to static electrification. In addition, we have further found that even when the moldings are recycled in a mode of re-melting them and re-molding the resulting melt, the thus-recycled moldings can still have good physical properties and are yellowed little. On the basis of these findings, we have completed the invention.
Specifically, the invention provides the following:
(1) A flame-retardant polycarbonate resin composition comprising (A) from 90 to 99.98% by weight of a polycarbonate resin, (B) from 0.01 to 5% by weight of an acid base-containing aromatic vinyl resin, and (C) from 0.01 to 5% by weight of a drip inhibitor, wherein the expression of % by weight is based on the total weight of (A), (B) and (C).
(2) The flame-retardant polycarbonate resin composition of (1), which comprises (A) from 97 to 99.96% by weight of a polycarbonate resin, (B) from 0.02 to 1% by weight of an acid base-containing aromatic vinyl resin, and (C) from 0.02 to 2% by weight of a drip inhibitor, wherein the expression of % by weight is based on the total weight of (A), (B) and (C).
(3) The flame-retardant polycarbonate resin composition of (1) or (2), wherein the acid base in the acid base-containing aromatic vinyl resin (B) is a metal sulfonate.
(4) The flame-retardant polycarbonate resin composition of any of (1) to (3), wherein the drip inhibitor (C) is at least one member selected from fluorine resins, silicone resins and phenolic resins.
(5) The flame-retardant polycarbonate resin composition of (4), wherein the drip inhibitor (C) is a fibril-forming polytetrafluoroethylene.
(6) A molding of the polycarbonate resin composition of any of (1) to 5), which is for housings or parts for electric or electronic appliances.